Contrasting physiological responses by cultivars of Oryza sativa and O. glaberrima to prolonged submergence.
OBJECTIVE
Oryza glaberrima is widely grown in flood-prone areas of African river basins and is subject to prolonged periods of annual submergence. The effects of submergence on shoot elongation, shoot biomass, leaf area and CO(2) uptake were studied and compared with those of O. sativa.


METHODS
A wide selection of lines of O. sativa and O. glaberrima, including some classified as submergence tolerant, were compared in field and pot experiments. Plants were submerged completely for 31 d in a field experiment, and partially or completely for 37 d in a pot experiment in a growth chamber.


RESULTS
Leaf elongation and growth in shoot biomass during complete submergence in the field were significantly greater in O. glaberrima than in O. sativa. So-called submergence-tolerant cultivars of O. sativa were unable to survive prolonged complete submergence for 31-37 d. This indicates that the mechanism of suppressed leaf elongation that confers increased survival of short-term submergence is inadequate for surviving long periods underwater. The O. sativa deepwater cultivar 'Nylon' and the 'Yélé1A' cultivar of O. glaberrima succeeded in emerging above the floodwater. This resulted in greatly increased shoot length, shoot biomass and leaf area, in association with an increased net assimilation rate compared with the lowland-adapted O. sativa 'Banjoulou'.


CONCLUSIONS
The superior tolerance of deepwater O. sativa and O. glaberrima genotypes to prolonged complete submergence appears to be due to their greater photosynthetic capacity developed by leaves newly emerged above the floodwater. Vigorous upward leaf elongation during prolonged submergence is therefore critical for ensuring shoot emergence from water, leaf area extension above the water surface and a subsequent strong increase in shoot biomass.
Sakagami
Jun-Ichi
J
Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan. sakajun@affrc.go.jp
Joho
Yukiko
Y
Ito
Osamu
O
D018533:Biomass; D055868:Floods; D005838:Genotype; D012275:Oryza / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology; D018520:Plant Shoots / Q000254:growth & development; D013997:Time Factors